The present invention relates to machines for the automatic production of filter bags containing a product for infusion, such as tea, camomile or other similar products, the filter bags being made of filter paper, folded and closed with a knotted thread which connects them to the pick-up tag.
In the packaging of products for infusion, the technique in which folded bags are formed and closed by knotting the thread connecting the filter bag and the pick-up tag is currently used to obtain top-quality bags of product, distinguished from similar bags by the fact that they prevent contact between the infusion and elements of the packaging which may, even to a limited degree, damage the health or (particularly important from a marketing viewpoint) modify the organoleptic characteristics of the infusion. Such effects are encountered, for example, in bags obtained by gluing sheets of filter paper with a hot-melt glue or even in bags in which the top is closed and the thread secured by metal staples.
In particular, the present invention relates to an improved machine of the type comprising a wheel which rotates with a stepping motion about its own axis of rotation and is equipped with grippers which, as the wheel rotates, are brought into contact with a series of operating stations around the wheel, which comprise, in particular, a station for folding a tubular semi-finished product consisting of filter paper containing the dosed product, and at least one station for knotting the thread so as to close the top of the bag and attach the pick-up tag to it. Such a machine is described in the application for an Italian patent BO95A000148.
A machine of the above-mentioned type fulfils the aim of allowing high-quality bags to be obtained. However, it can be significantly improved in terms of increasing its productivity.
The aim of the present invention is, therefore, to increase the production capacity of the machine through a corresponding increase in its operating speed.
Such an aim can be achieved by ensuring that the thread fed around the wheel, between the wheel and the operating stations, is not allowed to slide in an uncontrolled manner inside the machine, sliding which must be avoided, above all, during folding of the tubular section, when the thread is tensioned so as to circumscribe the filter bag being formed.
In accordance with the present invention, said aim is fulfilled by an improved machine comprising thread feed means which operate on the thread fed between pairs of grippers positioned one after another along the edge of the wheel.
If the machine, in accordance within a preferred embodiment comprises a knotting station equipped with a knotting device that has needles for knotting the thread to the tag and to the top of the filter bag, the needles being brought into contact with tag and bag-top stops and with respective mobile needle interceptor elements, the same aim can also be achieved by creating, in the knotting stations, between the needle, thread and interceptor elements, reciprocal connection conditions predetermined by precise geometric constraints which allow the obtainment of conditions which can be repeated with great precision, even when the machine is operating at high speed.
In accordance with the invention, the operating speed is increased by an improved machine in which the knotting device is equipped with at least one needle having a first and a second eye located at different distances from the point. Said needle, or needles being moved in such a way as to pick up the thread with the second eye, forming a loop in which the thread is associated with the first eye, an interceptor element being moved in time with the needle so that it passes through the first eye, pushing a section of thread through the above-mentioned loop.
In accordance with the invention, the above-mentioned aim is also achieved using a method for knotting the thread to the tag and to the top of the bag.
The technical features of the present invention, in accordance with the above-mentioned aims, are set out in the claims herein and the advantages more clearly illustrated in the detailed description which follows, with reference to the accompanying drawings, which illustrate a preferred embodiment without limiting the scope of application, and in which:
FIG. 1 is an assembly view of the improved machine according to the present invention;
FIG. 2 is a partial, scaled up view of the machine in FIG. 1, with some parts cut away to better illustrate others;
FIG. 2a illustrates a detail from FIG. 2;
FIGS. 3, 4 and 5 are schematic illustrations of a characteristic succession of operating stages of the machine according to the present invention;
FIGS. 6, 7 and 7a are a perspective assembly view, an elevation view and a scaled up detail of a filter bag made in the machine disclosed;
FIGS. 8, 9 and 9a are scaled up details of the machine, showing parts of the folding station in two elevation views (FIGS. 8 and 9) and a view from direction k in FIG. 9;
FIG. 10 is a scaled up detail view of the machine showing parts of the knotting station;
FIGS. 11 and 11A to 11M are detail views showing a succession of operating configurations of parts of the knotting station;
FIG. 12 is a plan view from below of an alternative embodiment of a detail of the invention;
FIG. 13 is a side elevation view of the detail illustrated in FIG. 12.